Secondary recovery method

ABSTRACT

Significant improvement in the recovery of hydrocarbons from a subterranean hydrocarbon-bearing formation containing acidsoluble components is accomplished by injecting into the formation via an injection well drilled into a formation communicating with an adjacent producing well and containing acid-soluble components which may or may not have water-sensitive clays and shales included therein, an aqueous acidic solution of an admixture as hereinafter described whereupon the acid component reacts with the acid-soluble components of the formation creating passageways or enlarging existing passageways thus facilitating the flow of fluids therein and the admixture prevents post-precipitation of dissolved salts and thereby increases the recovery of hydrocarbons from the formation through the adjacent producing well.

United States Patent Tate et al.

[ SECONDARY RECOVERY METHOD [75] Inventors: Jack F. Tate; Jim Maddox, Jr., both of Houston, Tex.

[73] Assignee: Texaco Inc., New York, NY.

[22] Filed: Dec. 26, 1973 [21] Appl. No: 428,486

[52] US. Cl 166/271; 166/274; 252/855 C [51} Int. Ci. E21B 43/22; E2113 43/27; E21B 43/26 [58] Field of Search l66/27l, 274, 275, 305 R, l66/308 [56] References Cited UNITED STATES PATENTS 3,724,544 4/1973 Tate l66/27l 3,811,505 5/1974 Flournoy et al. 166/274 Dec. 23, 1975 Primary EraminerStephen J. Novosad Assistant ExuminerGeorge A. Suckficld Attorney, Agent, or Firm-Thomas H. Whaley; Carl G. Ries; James F. Young [57] ABSTRACT Significant improvement in the recovery of hydrocarbons from a subterranean hydrocarbon-bearing formation containing acid-soluble components is accomplished by injecting into the formation via an injection well drilled into a formation communicating with an adjacent producing well and containing acid-soluble components which may or may not have watersensitive clays and shales included therein, an aqueous acidic solution of an admixture as hereinafter described whereupon the acid component reacts with the acid-soluble components of the formation creating passageways or enlarging existing passageways thus facilitating the flow of fluids therein and the admixture prevents post-precipitation of dissolved salts and thereby increases the recovery of hydrocarbons from the formation through the adjacent producing well.

14 Claims, N0 Drawings SECONDARY RECOVERY METHOD FIELD OF THE INVENTION well is increased by treating with an aqueous acidic solution of an admixture as hereinafter described thereby facilitating the flow of fluids through the formation resulting in increased hydrocarbon recovery via the production well.

DESCRIPTION OF THE PRIOR ART ln recovering oil from oil-bearing reservoirs it usually is possible to recover only a minor part of the original oil in place by the primary recovery methods which utilize the natural forces present in the reservoir. As a result, a variety of supplemental recovery techniques have been utilized to increase the recovery of oil from subterranean hydrocarbon-bearing reservoirs or formations. Although these supplemental techniques are commonly referred to as secondary recovery operations in fact they may be primary or tertiary in sequence of employment. In such techniques, a fluid is introduced into the formation in order to displace the oil therein to a suitable production system through which the oil may be withdrawn to the surface of the earth. Examples of displacing media include gas, aqueous liquids such as fresh water or brine, oil-miscible liquids such as butane, or a water and oil-miscible liquid such as an alcohol. Generally, the most promising of the secondary recovery techniques is concerned with 35 the injection into the formation of an aqueous flooding medium either alone or in combination with other fluids.

ln the application of these conventional procedures for the production of hydrocarbons from similar formations by the secondary recovery method of water-injection, one of the principal difficulties that has been encountered is the generally low production response realized because of the low penneabilities and the consequent low rate of water acceptance of the communicating formation. Thus, these unfavorably low responses both in injection rate and the overall production have led to the abandonment of hydrocarbon production by water-injection methods from many carbonate formations after only a minimal amount of the oilin-place has been produced.

One of the remedial measures that has been used frequently to increase water-injectivity in formations containing acid-soluble components is acid-treating of the injection wells to improve the permeability sur rounding the injection well bore, and thereby increasing the flow capabilities of the formation in the vicinity of the injection well bore. These measures, however, may result in only a temporary response in production improvement.

In acidizing an injection well utilizing the commonly employed procedure a non-oxidizing mineral acid, such as hydrochloric acid, is introduced into the injection well, and through the application of sufficient pressure is forced into the adjacent formation, where it reacts with the acid-soluble components, particularly the carbonates to dissolve them to form the respective salt of the acid, carbon dioxide and water, thereby increasing the permeability of the formation adjacent the bore of the injection well. The technique is not limited to application in formations of high acid solubility. Sandstone and gypsum-containing formations may require acidization if the injection water is unstable with respect to CaCO Fe(OH) or other salts.

If desired, the acidization may be carried out at an injection pressure sufficiently great to create fractures in the strata or formation which has the desired advantage of opening up passageways into the formation along which the acid can travel to more remote areas from the injection well bore. Conversely, fracturing a formation into which a displacing fluid is injected quite often is not desirable since sweep efficiency may be decreased and channelling occur. The salts formed upon neutralization of the acid are extensively water soluble and may pass through the formation dissolved in the displacing fluid.

There are, however, troublesome complications attending the use of hydrochloric acid, or other similar non-oxidizing material acids. In the acidizing process, the following primary beneficial reaction occurs:

CaCO ZHCI 010, up C0,? Under the higher pressures required to conduct an acidization, the CO, is dissolved in the reaction mixture consisting of spent acid and connate water:

Co, H,o+ i-nco, H H Hco; 214* The equilibria may be summarized and written:

After acidization is complete, the well is often returned directly to injection, the reaction products of the dissolution being forced into the formation in a solution of the displacing fluid. As the fluid moves away from the well bore, pressure diminishes allowing dissolved gasses such as CO to break out of solution, inducing insoluble carbonates, such as CaCO to postprecipitate. Similarly, acid-dissolved iron salts may be reprecipitate within the formation as hydrous iron oxides a distance from the well bore when pH rises due to exhaustion of the acid. In like manner, gypsum may precipitate if the injection fluid contains sulfate ion and if its temperature increases within the formation, since the gypsum has an inverse solubility relationship. Precipitation of this type when it occurs within the capillaries of a tight formation can serverly lessen the injection rate by plugging such capillaries.

It is known that molecularly dehydrated polyphosphates are effective in retarding CaCO precipitation. These polyphosphates are unsatisfactory in the method of the present invention because they undergo rapid hydrolysis in the presence of the mineral acid components. As a result, the scale inhibiting properties of these polyphosphates are destroyed. In addition, one hydrolytic reaction production, the phosphate ion (PO can precipitate with calcium or barium ions present in the produced water, causing additional plugging or scale deposition and further aggravating the problem. The so-called glassy" phosphates are known scale inhibitors. However, these glassy phosphates are unsatisfactory because of their slight solubility in acidic media and the tendency to form objectionable hydrolytic reaction products.

it is also known to employ various organic polymers 3 prevent the precipitation of the mineral salts. Many f these polymeric materials are unstable in mineral cids. In such acidic media they undergo spontaneous epolyamerization to an ineffective species. A repreentative polymeric material which undergoes hydrolyis in the presence of acids is polyacrylamide. in addiion, this polymer has a further disadvantage in that it is mstable in aqueous media at temperatures of about -F. and upwards. Many wells that are being treated iy the method of the present invention have bottom iole temperatures of 250300F. or higher.

The chemically altered natural polymers and natural )olymers themselves, are effective inhibitors to prevent he precipitation of mineral salts. However, some mate- 'ials such as sodium carboxymethylcellulose precipiate or decompose in the presence of mineral acids. )ther known sequestering agents such as citric or tar- ;aric acids, and/or complexing agents such as ethyleneiiaminetetraacetic acid and its water-soluble salts are rnown inhibitors to prevent the deposition of boiler scale in aqueous media. However, such materials are not applicable in the method of the present invention because they are not appreciably surface-active and do not adsorb on the formation face.

The primary object of the present invention is to provide a method for the improved recovery of hydrocarbon fluids from subterranean fluid-bearing formations wherein a composition comprising an aqueous acidic solution of an admixture as hereinafter described is injected into a formation communicating between a producing well and adjacent injection well, said formation containing acid-soluble components and in some instances also containing water-sensitive clays or shales, and whereafter the acid component of the said composition reacts with the acid-soluble components of the formation to increase permeability of the formation thereby facilitating the flow of fluids therethrough and the admixture component prevents the postprecipitation of compounds formed by the reaction of the acidic component with the formation.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a new and improved method for the recovery of hydrocarbons from subterranean hydrocarbon-bearing formations in which there is injected into the formation via an injection well drilled into a formation communicating with an adjacent producing well and containing acid-soluble components which may or may not have water-sensitive clays included therein, a composition comprising an aqueous acid solution of an admixture as hereinafter described which is capable of reacting with the acid-soluble components of the formation to increase the permeability thereof and the admixture component prevents precipitation of compounds formed by the said reaction of the acid component thereby permitting a substantial increase of production of hydrocarbons from the formation via the production well.

An advantage resulting in the treating subterranean hydrocarbon-bearing formations having acid-soluble components therein with the aqueous acidic solution of the admixture is that the post-precipitation of acid-dissolved salts is prevented or materially decreased. Such post-precipitation whether it be of carbonates from evolution of CO from solution, hydrous iron oxides from a rise in pH, or of gypsum from an increase in LII 4 formation temperature. can lead to plugging of formation capillaries and a consequent reduction of permeability. Such an event can reduce injectivity and accordingly the rate of production from adjacent wells.

DESCRIPTION OF THE INVENTION The method of the present invention in its broadest embodiment comprises introducing via an injection well drilled into a hydrocarbon-bearing formation containing acid-soluble components and communicating with a producing well a fluid composition comprising an aqueous acidic solution of an admixture as hereinafter described in amounts sufficient to react with the formation so as to increase substantiallyy the flow capability of the formation and to thereafter produce hydrocarbons from the said subterranean formation at an increased rate through the production well.

The admixture useful in preparing the aqueous acidic solution of the present invention is formed from about one part of weight of a sulfated/sulfonated polyethoxy alkyl phenol containing about 8 to about 14 carbon atoms in the alkyl group and from about 4 to about 19 ethoxy groups, together with from about I to 3 parts by weight of a C -C alkyl benzene sulfonic acid, including the alkali metal and ammonium salts of one or both compounds, as well as mixtures thereof.

Representative sulfated/sulfonated polyethoxy alkyl phenols include the octyl-, nonyl-, decyl-, undecyl-, dodecyl-, tridecyland tetradecyl-phenols ethoxylated with about 4 to about 10 ethoxy groups, such as the tetraethoxy-, hexaethoxy-, octaethoxyand decaethoxy adducts of the above nonyl phenols, the ammonium, sodium and potassium salts thereof. Particularly preferred compounds are sulfated/sulfonated tetraethoxylated nonyl phenol, sulfated/sulfonated hexaethoxylated nonyl phenol, and sulfated/sulfonated nonyl phenol containing an average of about 9.5 ethoxy groups therein.

Representative alkyl benzene sulfonic acids, including the straight and branched chain alkyl groups, useful in the practice of the invention include the octyl-, nonyl-, decyl-, undecyl-, dodecyl-, tridecyland tetradecyl-benzene sulfonic acids, the corresponding sodium, potassium and ammonium salts thereof as well as mixtures of one or more of said compounds. A preferred group is the C -C alkyl benzene sulfonic acids and the above salts thereof.

As used in the present specification and claims the expression "sulfated/sulfonated polyethoxy alkyl phenol" refers to the reaction product of a polyethoxy alkyl phenol described hereinabove with chlorosulfonic acid or sulfur trioxide for a time period of from about 5 to 90 minutes at a temperature in the range of from about 50to 60C., using a reactant mole ratio from about l mole of said phenol per 0.8 to 1.3 mole of said chlorosulfonic acid or sulfur trioxide.

Analysis of the resulting reaction products showed that from about to thereof was sulfated while the ID to 30% remaining was sulfonated. Accordingly, the term sulfated/sulfonated was used to describe this reaction product.

A preferred set of reaction conditions are from about 55 to about 60C., 30 to 90 minutes in time and mole ratios of from about 1 mole of said phenol per 1-1.3 mole of the chlorosulfonic acid or sulfur trioxide.

A preferred ratio of the admixture components is about one part by weight of the sulfated/sulfonated polyethoxy alkyl phenol to from about 1.25 to 2.75

parts by weight of the C C alkyl benzene sulfonic acid.

Preferably, the acidic aqueous treating composition of this invention injected into the hydrocarbon-bearing fomiation comprises an aqueous solution of from about 0.5 to about and preferably 1 to 6%, by weight of a non-oxidizing mineral acid, such as hydrochloric acid, etc., which contains therein between from about 0.005 to about 1% by weight, preferably from about 0.05 to .50% of the aforesaid admixture.

The aqueous acidic solutions employed in the method of this invention, preferably contain an inhibitor to prevent or greatly reduce corrosion attack on metals. A variety of such inhibitors are known in the art, e.g., certain compounds of arsenic, nitrogen or sulfur as described by Grebe et al. in US. Pat. No. l,877,504. Likewise, resin-amine type inhibitors, as illustrated in US. Pat. 2,758,970, may be utilized. A small but effective amount of the inhibitor is employed which generally ranges from about 0.02% to about 1.5% by weight of the aqueous solution.

In the first step of preparing the aqueous acidic composition of this invention, a solution containing the desired amount of a nonoxidizing mineral acid, such as hydrochloric acid, in water is prepared. An inhibitor to prevent corrosion on the metal equipment associated with the wells is usually added with mixing in the next step. The required amount of the admixture is then admixed with the aqueous acid solution.

The method of this invention can be carried out with a wide variety of injection and production systems which will comprise one or more wells penetrating the producing strata or formation. Such wells may be located and spaced in a variety of patterns which are well-known to those skilled in the art. For example, the so-called line flood" pattern may be used, in which case the injection and producing systems are composed of rows of wells spaced from one another. The recovery zone, i.e., that portion of the producing fom'iation from which hydrocarbons are displaced by the drive fluid to the production system, in this instance will be that part of the formation underlying the area between the spaced rows. Another pattern which is frequently used is the so-called circular flood in which the injection system comprises a central injection well while the production system comprises a plurality of production wells spaced about the injection well. Likewise, the injection and production systems each may consist of only a single well and here in the recovery zone will be that part of the producing strata underlying an elliptical-like area between the two wells which is subject to the displacing action of the aqueous drive fluid. For a more elaborate description of such recovery patterns reference is made to Uren, L.C., Petroleum Production Engineering-Oil Field Exploitation, Second Edition, McGraw Hill Book Company, Inc., New York, 1939, and to US. Pat. Nos. 3,472,3l8 and 3,476,182.

In carrying out the method of this invention, the aqueous acidic solution of the admixture is forced, usually via a suitable pumping system, down the well bore of an injection well and into the producing formation through which it is then displaced together with hydrocarbons of the formation in the direction of a production well. As those skilled in the art will readily understand, the pressure employed is determined by the nature of the formation, viscosity of the fluid, and other operating variables. The acidization method of this invention may be carried out at a pressure sufiicient merely to penetrate the formation or it may be of sufficient magnitude to overcome the weight of the overburden and create fractures in the formation. Propping agents, to prop open the fractures as created, for example 20 to 60 mesh sand in accordance with known fracturing procedures, may be also employed with the aqueous acidic solution containing the admix ture.

The formation may be treated continuously with the specific solution of such treatment may be temporary. If desired, however, after a time, conventional flooding may be resumed. The aqueous acidic solution of the admixture also may be applied in a modified water flood operation in which there is first injected into the well bore a slug of the aqueous acidic solution of admixture which is forced under pressure into the subterranean formation. The first step is then followed by a similar injection step wherein a slug of an aqueous drive fluid, such as water, is injected, which is thereafter followed by a repetition of the two steps. This sequence may be repeated to give a continuous cyclic process. The size of the slugs may be varied within rather wide limits and will depend on a number of conditions, including the thickness of the formation, its characteristics and the conditions for the subsequent injection of the aqueous drive medium.

In the method of this invention, the admixture component of the composition provides means whereby ions produced by the reaction of the acid component with the formation having tendencies to precipitate as salts such as CaCO hydrous iron oxides and CaSO ZH O, combine with admixture to form a highly stable complex therewith so that solid salts do not precipitate from the spent treating solution. This binding up of the aforementioned ions from weakly ionizable compounds permits the formed complex to remain dissolved in the treating solution and pass through the formation pores. Further, the admixture component of the composition provides means whereby the nucleation and growth of the solid itself is thwarted, so that solid salts do not precipitate from the spent treating solution. Finally, the admixture component of the composition provides means whereby continuous protection against postprecipitation of salts is obtained for considerable period of time subsequent to treatment due to continuous slow desorption of the admixture from the formation faces. In contrast, use of surfactants having merely dispersant and suspending properties and not possessing the capability of molecularly binding up these produced ions or thwarting the nucleation and growth of solid salts thereof will permit post-precipitation of said salts from such treating solution with the likelihood of plugging up the formation passageways during subsequent recovery of desirable formation hydrocarbons therethrough.

It should be understood that the concentrations of the admixture and the acid components are chosen to provide a displacing fluid of the desired rheological properties. Similarly, the appropriate admixture is selected on the basis of the formation being treated as well as other operating conditions employed.

The use of acid concentrations above about 15% is unsatisfactory since high concentrations result in the hydrolysis of the sulfated/sulfonated ethoxy alkyl phenol component of the admixture.

If desired one can also add to the aqueous acidic solution containing the admixture a polymeric material to retard the acid components tendency to attack the 7 calcareous components of the formation. Suitable a polyvinylpyrrolidone as more particularly described in U.S. Pat. No. 3,749,169, issued July 3 l, i973 is particularly desirable and the disclosure of said patent is herein incorporated by reference.

EXAMPLE 1 Through a water injection well drilled into a limestone formation there is displaced under pressure down the tubing and into the formation an aqueous 3% by weight hydrochloric acid solution containing 1% by weight, based on the total weight of the solution, of an admixture consisting of sulfated/sulfonated tetraethoxy nonyl phenol and ammonium dodecyl benzene sulfo nate, each being present in a l/l ratio. The pressure required to inject the required volume of water declines considerably and no increase in said pressure is noted subsequent to treatment indicating that postprecipitation of CaCO within the formation leading to permeability reduction is prevented or materially lessened. The well is then returned to conventional water injection. After about 30 days the production of hydrocarbons from an adjacent producing well is substantially increased.

EXAMPLE ll A flooding operation is carried out in an oil-containing reservoir in accordance with the process of this invention. Four injection wells are arranged in a rectangular pattern around a single centrally located production well in this system. A slug consisting of 75 barrels of an aqueous acidic solution containing 0.5% by weight, based on the total weight of the solution, admixture as Example l, in a 3% by weight hydrochloric acid, is displaced via each of the four injection wells into the formation at a rate of about 50 bbl/day. In the next step, 100 barrels of water are injected under pressure into the producing formation through each injection well at a rate of about 55 bbl/day. This sequence of operations is repeated numerous times and the result is an increased injection rate of the drive streams into the injection wells and a subsequent increase in the rate of production of hydrocarbons via the production well.

EXAMPLE [II An injection well in a fonnation containing about 20% HO soluble material is treated with 500 gallons of conventional l% HCI followed by 1500 gallons of 3% HC] containing an admixture consisting of a sulfatedlsulfonated nonyl phenol ethoxylated with about 9.5 ethylene oxide groups and sodium decyl benzene sulfonate in a l/ 1 weight ratio. The aqueous acidic admixture is displaced from the tubing into the formation with least water and the well shut in for 24 hours. Thereafter the well is returned to water injection. The injectivity of the well is materially increased for a sustained period of time resulting in enhanced hydrocarbon recovery.

It is significant that the admixture is an effective material in the presence of high calcium ion concentra tions of the order of up to 10,000 ppm or more, for the sulfated/sulfonated polyethoxy alkyl phenols are relatively ineffective and the alkyl benzene sulfonic acids alone are not satisfactory at calcium ion concentrations above about 50 ppm. The admixture appears to stabilize the alkyl benzene sulfonic acid component.

Obviously, many modifications and variations of the invention as heretoabove set forth may be made with- 8 out departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A method for the recovery of hydrocarbons from a hydrocarbonbearing formation containing acid-soluble components having at least one injection well and at least one production well penetrating the said formation and a fluid communication, which comprises displacing through the formation and aqueous acidic solution of 0.5 to 15% by weight of a non-oxidizing mineral acid and from about 0.0005 to about 1% by weight of an admixture therein, and recovering hydrocarbons through the production well, said admixture being formed from about one part by weight of (A) a member selected from the group consisting of a sulfated/sulfonated polyethoxy alkyl phenol containing from about 8 to about 14 carbons atoms in the alkyl group and from about 4 to about 10 ethoxy groups, the corresponding alkali metal and ammonium salts and mixtures thereof, with (B) from about 1 to about 3 parts by weight of a member selected from the group consisting of a C -C alkyl benzene sulfonic acid, the corresponding alkali metal and ammonium salts and mixtures thereof.

2. Method as claimed in claim 1 wherein said admixture is present in said aqueous acidic solution in an amount of from about 0.05 to about 0.5% by weight.

3. Method as claimed in claim 1 wherein said admixture is fon'ned from about one part by weight of said sulfated/sulfonated polyethoxy alkyl phenol to from about 1.2 to 2.75 parts by weight of said C C alkyl benzene sulfonic acid.

4. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated tetraethoxy nonyl phenol and ammonium dodecyl benzene sulfonate.

5. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated hexaethoxy nonyl phenol and sodium decyl benzene sulfonate.

6. Method as claimed in claim 1 wherein said admixture is composed o sulfated/sulfonated octaethoxy nonyl phenol and ammonium dodecyl benzene sulfonate.

7. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated polyethoxy nonyl phenol wherein the average number of ethoxy groups therein is about 9.5, and sodium decyl benzene sulfonate.

8. Method as claimed in claim 1 wherein said acid is present in the solution in an amount of from about 1 to about 6% by weight.

9. Method as claimed in claim 1 wherein said acid is hydrochloric acid.

10. Method as claimed in claim I wherein said acid is sulfuric acid.

ll. Method as claimed in claim 1 wherein said acid is present in the solution in an amount of from about I to about 3% by weight.

12. Method as claimed in claim 1 wherein the said solution is injected down the injection well bore penetrating said formation under a pressure greater than the formation pressure and sufficient to create fractures in the formation.

13. Method as claimed in claim 1 wherein the said solution is injected down the well bore penetrating said formation under a pressure greater than formation pressure but less than the pressure required to create 9 fractures in the formation.

14. A method for the recovery of hydrocarbons from a hydrocarbon-bearing formation containing acid-soluble components and having at least one injection well and at least one production well penetrating the said formation in fluid communication, which comprises displacing through the formation a slug of an aqueous acidic solution of 0.5 to 6% by weight of hydrochloric acid and from about 0.05 to about 0.5% by weight of an admixture therein, said admixture being formed from about one part by weight of (A) a member selected from the group consisting of a sulfated/sulfonated polyethoxy alkyl phenol containing from about 8 to about UNITED STATES PATENT AND TRADEMARK ()FEICE CER'HFICATE 0F QGREQHQN PATENT NO. 3,927,718

DATED December 23 1975 INVENTOR(S) Jack F. Tate and Jim Maddox, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 55 after "acid-treating of" omit the Col. 2, line 42 after "salts may" omit be Col. 2, line 60 delete "production" and insert product Col. 3, line 61 after "resulting in" omit the line 20 delete (1st occurrence) and insert by Col. 4, line 21 after "containing" insert from Col. 6, line 32 after "combine with" insert the Col. 6, line 44 after "obtained for" insert a Col. 6, line 63 after "unsatisfactory since" insert such Col, 7, line 1 delete "Suitable" and insert Suitably Col. 7, line 54 delete "least" and insert lease Col. 8, line 10 delete "and" and insert an gned and fieaied this Fourteenth Day 9f November 1978 {SEAL} Arrest:

R C MASQN DONALD W. BANNER Arresting 0M? Cammissioner ofPateuts and Trademarks UNITED STATES PATENT AND TRADEMARK UFFICE QEER'EEFEQATE @F RT$N PATENT NO. I 3,927,718

. DATED December 23, 1975 !NVENTOR(S) Jack F. Tate and Jim Maddox, Jr.

it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Q Col. 1, line 55 after "acid-treating of" omit the Col. 2, line 42 after "salts may omit be Col. 2, line 60 delete "production" and insert product Col, 3, line 61 after "resulting in" omit the line te (1st occurrence) and insert by Col. 4, line 21 after "containing" insert from Col 6, line 32 after "combine with" insert the Col, 6, line 44 after "obtained for" insert a Cole 6, line 63 after "unsatisfactory since" insert such Col. 7, line 1 delete "Suitable" and insert Suitably Col, 7, line 54 delete "least" and insert lease Cole 8, line 10 delete "and" and insert an O and firaied this Fmerteeaith Q; November 1978 {SEAL} 6 Assess:

D N RUTH a MAsON 0 ALB W BANNER Atesoizeg Gflieey Commissioner of Patents and Trademarks C UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,927,718

DATED December 23 1975 lNVENTOR(S) Jack F. Tate and Jim Maddox, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 55 after "acid-treating of" omit the Col. 2, line 42 after "salts may" omit be Col. 2, line 60 delete "production and insert product Col. 3, line 61 after "resulting in omit the line 20 delete "O (1st occurrence) and insert by Col. 4, line 21 after "containing" insert from Col. 6, line 32 after "combine with" insert the Col. 6, line 44 after "obtained for" insert a Col. 6, line 63 after "unsatisfactory since" insert such Col. 7, line I. delete "Suitable" and insert Suitably Col. 7, line 54 delete "least" and insert lease Col. 8, line 10 delete "and" and insert an Signed and Scaled this Fourteenth Day of November 1978 {SEAL} Anew.-

RUTH MASON DONALD W. BANNER Amalia; Oflicev Commissioner ofPuteuts and Trademarks 

1. A METHOD FOR THE RECOVERY OF HYDROCARBONS FROM A HYDROCARBON-BEARING FORMATION CONTAINING ACID-SIKYVKE CINOINENTS HAVING AT LEAST ONE INJECTION WELL AND AT LEAST ONE PRODUCTION WELL PENETRATING THE SAID FORMATION AND A FLUID COMMUNICATION, WHICH COMPRISES DISPLACING THROUGH THE FORMATION AND AQUEOUS ACIDIC SOLUTION OF 0.5 TO 15% BY WEIGHT OF A NON-OXIDIZING MINERAL ACID AND FROM ABOUT 0.005 TO ABOUT 1% BY WEIGHT OF AN ADMIXTURE THEREIN, AND RECOVERING HYDROCARBONS THROUGH THE PRODUCTION WELL, SAID ADMIXTURE BEING FORMED FROM ABOUT ONE PART BY WEIGHT OF (A) A MEMBER SELECTED FROM THE GROUP CONSISTING OF A SULFATED/SULFONATED POLYETHOXY ALKYL PHENOL CONTAINING FROM ABOUT 8 TO ABOUT 14 CARBONS ATOMS IN THE ALKYL GROUP AND FROM ABOUT 4 TO ABOUT 10 ETHOXY GROUPS, THE CORRESPONDING ALKALI METAL AND AMMONIUM SALTS AND MIXTURES THEREOF, WITH (B) FROM ABOUT 1 TO ABOUT 3 PARTS BY WEIGHT OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF A C8-C14 ALKYL BENZENE SULFONIC ACID, THE CORRESPONDING ALKALI METAL AND AMMONIUM SALTS AND MIXTURES THEREOF.
 2. Method as claimed in claim 1 wherein said admixture is present in said aqueous acidic solution in an amount of from about 0.05 to about 0.5% by weight.
 3. Method as claimed in claim 1 wherein said admixture is formed from about one part by weight of said sulfated/sulfonated polyethoxy alkyl phenol to from about 1.2 to 2.75 parts by weight of said C8-C14 alkyl benzene sulfonic acid.
 4. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated tetraethoxy nonyl phenol and ammonium dodecyl benzene sulfonate.
 5. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated hexaetHoxy nonyl phenol and sodium decyl benzene sulfonate.
 6. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated octaethoxy nonyl phenol and ammonium dodecyl benzene sulfonate.
 7. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated polyethoxy nonyl phenol wherein the average number of ethoxy groups therein is about 9.5, and sodium decyl benzene sulfonate.
 8. Method as claimed in claim 1 wherein said acid is present in the solution in an amount of from about 1 to about 6% by weight.
 9. Method as claimed in claim 1 wherein said acid is hydrochloric acid.
 10. Method as claimed in claim 1 wherein said acid is sulfuric acid.
 11. Method as claimed in claim 1 wherein said acid is present in the solution in an amount of from about 1 to about 3% by weight.
 12. Method as claimed in claim 1 wherein the said solution is injected down the injection well bore penetrating said formation under a pressure greater than the formation pressure and sufficient to create fractures in the formation.
 13. Method as claimed in claim 1 wherein the said solution is injected down the well bore penetrating said formation under a pressure greater than formation pressure but less than the pressure required to create fractures in the formation.
 14. A method for the recovery of hydrocarbons from a hydrocarbon-bearing formation containing acid-soluble components and having at least one injection well and at least one production well penetrating the said formation in fluid communication, which comprises displacing through the formation a slug of an aqueous acidic solution of 0.5 to 6% by weight of hydrochloric acid and from about 0.05 to about 0.5% by weight of an admixture therein, said admixture being formed from about one part by weight of (A) a member selected from the group consisting of a sulfated/sulfonated polyethoxy alkyl phenol containing from about 8 to about 14 carbon atoms in the alkyl group and from about 4 to about 10 ethoxy groups, the corresponding alkali metal and ammonium salts and mixtures thereof, with (B) from about 1 to about 3 parts by weight of a member selected from the group consisting of a C8-C14 alkyl benzene sulfonic acid, the corresponding alkali metal and ammonium salts and mixtures thereof, thereafter injecting a slug of an aqueous drive fluid into the formation to drive the said solution through the formation toward said production well and recovering hydrocarbons through the production well. 